The Rhizoctonia Damping-Off of Conifers 15 



obtained in a few cases from white-pine seedlings that had been killed 

 several weeks previous to the time of collection. These miscellaneous 

 organisms undoubtedly represented saprophytic development in seedlings 

 already killed by the damping-off fungus. 



The data in table 3 further indicate that Rhizoctonia was the chief 

 organism associated with diseased seedlings obtained from the Milton, 

 the Gerrish, and the Amherst nurseries, although Fusarium and Alternaria 

 were both found to a lesser extent in one or more cases. Microscopic 

 examination, however, showed that Rhizoctonia was more abundant than 

 the other two organisms in the diseased tissues. The data for the other 

 three nurseries are less detailed, but indicate that Fusarium was predomi- 

 nant in the diseased seedlings. Pythium was abundant in the seedlings 

 from the St. Williams nursery. These specimens were in a rather advanced 

 state of decay when they were received. 



Inoculation and reisolation studies 



When inoculation studies were first begun during the winter of 1925-26, 

 the method employed was that of growing the seedlings in three-inch 

 pots of unsterilized soil to which small amounts of inoculum had been 

 added. Five pots were used for each organism, and three served as checks. 

 The inoculum was prepared by growing the fungus for three or more weeks 

 in flasks of steamed wheat kernels. Ordinary tap water was employed 

 in sprinkling. In these experiments, considerable damping-off occurred 

 in many of the check pots. Because of this, all subsequent tests were 

 made in steam-sterilized soil and the number of check pots was increased 

 from three to five. The pots were filled two-thirds full with a rather 

 heavy loam, and steam-sterilized for two to three hours at 25 pounds 

 pressure, following which 5 grams of inoculum was added to each pot. 

 The inoculum was covered with a half-inch layer of a sterilized muck and 

 sand mixture, and sufficient seed was sown to produce from twenty to 

 forty seedlings per pot. The seed was covered with a thin layer of either 

 sand or muck. During the winter of 1926-27, only distilled water was 

 used in sprinkling, while ordinary tap water was employed during the 

 following season. 



For the first two winters the mean daily temperature of the greenhouse 

 varied from 65° to 75° F., while for the third season automatic controls 

 maintained a fairly uniform temperature of approximately 65° F. 



Since the methods thus varied somewhat during the three winters, it 

 should be pointed out that all of the Pythium strains and most of the other 

 fungi from the Ithaca nursery were tested during 1925-26. The majority 

 of the Rhizoctonia strains from the Keene nursery were tested in 1926-27, 

 and all other fungi in 1927-28. 



The results obtained from inoculation experiments with more than a 

 hundred strains of fungi are brought together in table 4. While records 



